T. C. Tisone

The origin of internal stress in low−voltage sputtered tungsten films

The internal stress can be of importance in the tungsten metallization process used for the fabrication of large−scale integrated circuits. The present work is an extension of an earlier study on the dependence of the stress in low−voltage triode sputtered tungsten films upon deposition conditions and substrate materials. As a function of film thickness, the stress was found to decrease with increasing thickness at various substrate temperatures. The effect of higher substrate temperatures is just to change from large compressive stress to smaller compressive stress and finally into tension. For example, the stress in a 5000−A film decreases from 1.6×1010 dyn/cm2 in compression to 5×109 dyn/cm2 in tension as substrate temperature increases from 370 to 850 °C. Generally, no gross difference was found for films deposited on SiO2, Al2O3, or Si3N4 at higher substrate temperatures. As a function of deposition rate, the stress can be described in three regions. The stress was found to be small and relatively co...

Internal stresses and resistivity of low‐voltage sputtered tungsten films

The continuing development of microelectronic circuits toward greater complexity has stimulated interest in new materials and processes compatible with the currently known silicon device technology. Tungsten has been considered as the first‐level conductor for a multilevel structure due to its relatively low electrical resistivity, its thermal expansion coefficient which matches fairly well to that of silicon, its demonstrated good adherence to the dielectrics of interest, and its ability to withstand high‐temperature processing. The present work is a part of a study of the dependence of the properties of low‐voltage triode sputtered tungsten films upon deposition parameters. The effects on internal stress and resistivity of tungsten films are reported here. Tungsten films have been deposited with thicknesses from 1000 to 15000 A and with resistivities as low as 8 μω cm (1.55 of the bulk). These films were deposited at 1 μ argon pressure at rates in the range of 50–400 A/min. The electrical resistivity wa...

Interdiffusion and compound formation in Ta--Au thin-film couples

An investigation of the interdiffusion between sputter‐deposited bilevel films of bcc Ta–Au, β‐Ta–Au, and Ta2N–Au has been carried out by using x‐ray diffraction, electron microscopy, and electrical resistance measurements. In all three systems only the TaAu phase was observed to form. The temperature range of formation of the TaAu phase for the systems considered increased in the order β‐Ta, bcc Ta, and Ta2N. The resistance change for a given temperature increased in the order Ta2N, bcc Ta, and β‐Ta. It was concluded that the change of resistance occurred by three mechanisms: (1) diffusion of Ta into the Au grain boundaries, (2) diffusion of Ta into the Au bulk, and (3) transformation of the Au into a high‐resistivity TaAu phase. From the resistance measurements the kinetics of the formation of the TaAu phase were found to be diffusion controlled with the diffusion species moving through the TaAu phase grain boundaries.

Metallurgical Control of Magnetic Properties in Co–Fe and Ni–Fe Alloys for Memory Applications

Magnetic memories such as the Twistor require materials which exhibit a square hysteresis loop, controlled value of coercive force, and low stress sensitivity of the magnetic properties. Recent work on optimizing these properties in Co–Fe and Ni–Fe alloys as storage and sensing elements, respectively, will be reviewed. Co–Fe alloys in the face‐centered cubic phase (∼90% Co) exhibit low values of magnetostriction and high values of magnetocrystalline anisotropy with 〈111〉 easy axes. Square hysteresis loops are obtained in cold‐drawn wires and tapes roll flattened from such wires, as a sharp 〈111〉 axial texture is developed by the cold working. With alloying additions such as Au and Ti, values of coercive force up to 42 Oe can be attained via precipitation aging. For Ni–Fe alloys near the 4% Mo–79% Ni composition, a predominant 〈111〉 axial texture is developed in wire drawing and is converted to 〈100〉 via recrystallization anneal. Since the magnetostriction and magnetocrystalline anisotropy constants are ne...

Elastic Moduli of Cobalt‐Iron Single Crystals

Face‐centered‐cubic (fcc) Co–Fe alloys in the vicinity of 10 at. % Fe form the basis for an important class of semihard magnetic alloys used for memory and switching applications. The elastic properties are important in determining the magnitude of the internal and/or applied stresses resulting from device operation and processing. The work described was undertaken to evaluate the compositional dependence of the elastic stiffness moduli in the fcc range of stability. The elastic stiffness moduli for single crystals of 6, 12, and 14 at. % Fe were measured by an ultrasonic method previously described (Ref. 3). The results for the 6 at. % Fe alloy at 25°C were c11=2.340, c12=1.589, and c44=1.259×1012 dyn/cm2. The stiffness moduli were found to vary only slightly with composition.

Stress insensitive permalloys for memory application

A description of the development of a family of high-squareness low-stress-sensitivity Permalloys of controlled coercive force for application as the soft magnetic element in the piggyback twister-type memory is given. Since both the hard- and soft-magnetic elements are wrapped simultaneously around the conductor core, the magnetic properties of both elements must be optimized by a single post-wrap annealing treatment. Previous work on a Co-Fe-Au alloy as the hard magnetic element has led to an annealing temperature range of 800-900°C, which must now be adopted for the treatment of the soft magnetic element as well. From published data on the compositional dependence of magnetocrystalline anisotropy and saturation magnetostriction in Ni-Fe-Mo alloys, an optimum composition, 6 percent Mo-80.5 percent Ni-13.5 percent Fe was first devised for which dB_{r}/d\sigma \simeq 0, B_{r}/B_{s} > 0.9 , and H_{c} \simeq 0.3 Oe after post-wrap annealing. By adding small amounts of Be (0.4-0.7 percent) or Zr (0.2-0.4 percent), the coercive force can be controlled to any value up to 3 Oe as a result of precipitation. At the same time, low stress sensitivity was retained and squareness improved.